Digger Wasps

Life History of a Digger Wasp
(Sphecius speciuosus Say.)
This large and ferocious wasp, which is in fact the largest wasp in what may be termed the eastern central states, that is to say, from southern New Jersey southward, is very abundant in Maryland, and Virginia and the mid-western states in the month of July, digging great burrows, usually in clayey soils, and storing in them for food the large dog-day Cicada, harvest-fly or lyre-man, or annual Cicada (Tibicen pruinosa Say). During the latter half of July, when the note of the Cicada is tilling the air with its vibrations, this big wasp is often seen flying about the trees from which the song comes. Suddenly the regular note of the harvest-fly ceases and in its stead a distressing, discordant cry will be emitted. The wasp has caught its victim and with a quick sting has paralyzed it and thrown it into a comatose condition from which it never recovers.

In this preliminary struggle often both the wasp and its victim fall to the ground and then the wasp begins the laborious task of dragging its prey back up the tree straddling it with its long legs, although the Cicada is bigger than the wasp, and working sometimes for an hour or more until it reaches a height from which it can fly obliquely down to its nest at some distance away. In Washington, the dryer and more elevated portions of the lawns, especially slight terraced along the sides of roadways, are preferred by this wasp for its burrows.

Damp earth causes the Cicadas to mould after they have been stored in the burrow. The burrow itself consists of a gently sloping entrance extending for about six inches, when ordinarily a turn is made at right angles and the excavation is continued for six or eight inches farther, ending in a globular cell an inch and a half in diameter. Frequently a number of branches leave the main burrow at about the same point, each terminating in a round cell. Each of these cells contains, along in August, one or two Cicadas, and in those cells which contain two the larva of the wasp acquires a larger size, and, as the female wasp is a great deal larger than the male, Riley thought that one Cicada is required as food to develop a male and two to develop a female.

The delicate, white, elongate egg of the wasp is laid under the middle leg of the Cicada and when it hatches the larva sticks out its head and begins at once to draw nourishment from between the segments of its victim. The egg hatches in two or three days and the a little more. It feeds larva attains full growth in a week, or entirely from the outside and when full grown spins awhile silken cocoon which is finished at the expiration of two days. The word silken is somewhat misleading, since it is mixed with much earth. When it is finished, about a dozen curious, parklike openings are seen in the side of the cocoon, the function of which can only be surmised. Possibly they are for the respiration of the larva before it transforms to pupa and it remains in the cocoon unchanged through the winter, transforming to pupa only the following spring and shortly before the appearance of the true insect. When the adult hatches it gnaws its way out of the cocoon and so on up through the burrow to the surface of the ground, thus accomplishing its life-round in a full year. This big digger wasp is very abundant in mid-summer throughout the southern states. It stings severely, and, it is perhaps needless to say, should be avoided.